1. Technical Field
The present invention relates to a projector using a fixed pixel display device, and an image processing device included in the projector.
2. Related Art
A projector, which uses a fixed pixel display device such as a liquid crystal panel or a DMD (Digital Micromirror Device, a trademark of Texas Instruments, Inc.) to project an image formed on the fixed pixel display device onto a screen, has been put into practical use.
FIG. 7 is an illustration showing an outline of a process executed in a case in which an image is projected by a heretofore known projector.
In the heretofore known projector, an execution of an image process which converts a resolution of an input image (hereafter referred to as a “resolution conversion process” or simply as a “resolution conversion”) is carried out in order to match the resolution of the input image with a resolution of a fixed pixel display device, as well as adjust a size of a projection image projected onto a screen (hereafter referred to also as a “projection size”). Also, in the same way, in the heretofore known projector, an execution of an image process which transforms a shape of an image formed on the fixed pixel display device (hereafter referred to also as a “keystone process”) is carried out in order to correct a distortion occurring in the projection image (hereafter referred to as a “projection distortion” or a “keystone distortion”) in accordance with a projection angle with respect to the screen. In this specification, the “resolution” means a number of dots (a number of pixels) in a horizontal direction, and a number of lines (a number of scanning lines) in a vertical direction, of the image or the fixed pixel display device. Then, there is also a case of referring to the number of dots in the horizontal direction as a “horizontal resolution”, and the number of lines in the vertical direction as a “vertical resolution”.
Specifically, as shown in FIG. 7, the resolution conversion process is executed in a resolution converter, and the keystone process is executed in a keystone processor. The resolution converter, with the resolution of the fixed pixel display device (in this example, “1024′768 dots”) as a reference (hereafter referred to also as a “reference projection size”), executes the process of converting a resolution of an image (the input image) represented by image data included in an input image signal (hereafter referred to also as “input image data), in accordance with a desired projection size (in this example, “about 79%”) preset at the reference projection size or smaller, and generates image data (hereafter referred to also as a “display image data”) representing an image to be displayed (hereafter referred to also as a “display image”) which has a resolution (a resolution “800′600 dots” corresponding to the projection size “about 79%”) lower than or equal to the resolution of the fixed pixel display device. Then, the keystone processor executes a correction process (the keystone process) according to the projection angle with respect to the screen on the display image data, and generates image data having the projection distortion corrected (hereafter referred to also as “keystone correction image data”). By forming an image represented by the generated keystone correction image data (hereafter referred to also as a “keystone correction image”) on the fixed pixel display device as a projection image, the projection image having the projection size adjusted and the projection distortion corrected is displayed on the screen.
Herein, the resolution conversion process in the resolution converter and the keystone process in the keystone processor are each executed within a time period, from a start time to a finish time of the image formation on the fixed pixel display device, within each frame period represented by a predetermined vertical period (generally referred to as a “frame period”) which serves as a reference for forming the image on the fixed pixel display device. At this time, the higher a resolution conversion ratio (an upscaling ratio or a downscaling ratio), the higher a processing speed in the resolution converter is required to be. Also, in the same way, the greater the projection angle, the higher a processing speed in the keystone processor is required to be. In addition, as the keystone processor executes the keystone process, using the image data transmitted from the resolution converter, it having to wait until resolution converted image data necessary for the process are transmitted from the resolution converter as the display image data, a still higher speed is required of it depending on a length of the wait time.
Herein, for example, in a case of a kind of projection angle in which a resolution conversion ratio in the resolution converter is halved in a vertical direction, and an image transformation ratio in the keystone processor is halved in a vertical direction, the resolution converter carries out a process of converting horizontal 4-line input image data into 2-line resolution converted data, and transmits them. Also, the keystone processor carries out a process of transforming the horizontal 2-line resolution converted data from the resolution converter into 1-line keystone correction image data, and transmits them. Consequently, it follows that the keystone processor carries out the process of transforming the horizontal 4-line input image data directed to the resolution converter into the 1-line keystone correction image data, and transmits them, and that it is required to have a processing speed four times higher than in a case of carrying out neither the resolution conversion nor the keystone process. For this reason, in the event that a possible processing speed in the keystone processor is lower than the fourfold processing speed, a projection is impossible at an angle corresponding to this. Consequently, the heretofore known projector responds by setting a restriction on a projection angle range, based on the possible processing speed in the resolution converter or the keystone processor. For this reason, it is desired to ease the restriction on the projection angle range and expand the projection angle range.
As a simple method of expanding the projection angle range, it is conceivable to dispose a frame memory between the resolution converter and the keystone processor. However, this method is undesirable as it requires a memory for at least one frame, causing an increase in a manufacturing cost.
Examples of the related art include JP-A-2003-84738, JP-A-2005-210418 or JP-A-2001-177787.